Conventionally, an imaging device has been known which is provided with a first case having a lens member attached to one end thereof and an opening at the other end thereof, a substrate accommodated in the first case, the substrate having a female terminal which is electrically connected to an imaging element, a second case assembled to the first case so as to close the opening of the first case, and a male terminal that is mounted on the second case so as to be electrically connected to the female terminal when the second case is assembled to the first case. In the imaging device, a connector is formed by the male terminal and the female terminal (refer to Patent Literature 1, for example).
Further, in recent years, to improve the data transmission speed from a lens unit disposed inside the imaging device to an image processing unit disposed outside the imaging device, consideration has been made to use a single coaxial cable to transmit operating power and a control signal from the image processing unit to the lens unit and also to adopt power supply superposition that is used to transmit an image signal from the lens unit to the image processing unit.
As a related connector that is used to electrically connect the coaxial cable and the lens unit, an SMB connector as shown in FIG. 5 is provided. An SMB connector 101 in FIG. 5 has a receptacle 103 that is mounted on a substrate 102 and a plug 104 that is electrically attached to a coaxial cable, which is not shown in the drawings, and is fitted into the receptacle 103.
The receptacle 103 has a needle-shaped central conductor portion 103a, a tubular outer conductor portion 103b that concentrically surrounds the central conductor portion 103a, and an insulator 103c that electrically insulates the central conductor portion 103a from the outer conductor portion 103b. In the receptacle 103, a groove portion 103d is formed to extend in a connector circumferential direction on an outer peripheral surface of the outer conductor portion 103b. 
The plug 104 has a plurality of inner contact pieces 104a that make contact with an outer peripheral surface of the central conductor portion 103a when the plug 104 is fitted into the receptacle 103, a plurality of outer contact pieces 104b that extend in a connector axial direction along the outer peripheral surface of the outer conductor portion 103b when the plug 104 is fitted into the receptacle 103, an insulator 104c that electrically insulates the inner contact pieces 104a from the outer contact pieces 104b, and a tubular housing portion 104d that surrounds the plurality of outer contact pieces 104b in a circumferential direction. In the plug 104, bent portions 104e are formed on the outer contact pieces 104b to be fitted into the groove portion 103d. 
An inner conductor of the coaxial cable, which is not shown in the drawings, is electrically connected to the inner contact pieces 104a of the plug 104 and an outer conductor of the coaxial cable, which is not shown in the drawings, is electrically connected to the outer contact pieces 104b of the plug 104. When the plug 4 is fitted into the receptacle 103, the inner conductor of the coaxial cable becomes conductive to the central conductor portion 103a via the inner contact pieces 104a and the outer conductor of the coaxial cable becomes conductive to the outer conductor portion 103b via the outer contact pieces 104b and the bent portions 104e. 